The present invention relates to screw-type resin injection apparatuses for injection molding and, more particularly, to a screw-type resin injection apparatus for use in an in-line screw-type injection molding system.
An in-line screw-type injection molding system has a screw-type resin injection apparatus for injecting and filling resin (resinous material) into a cavity in a forming mold. Generally, the screw-type resin injection apparatus comprises an injection cylinder element defining therein an injection cylinder chamber and having, at one end thereof, a resin injection nozzle, an injection screw arranged within the injection cylinder chamber in a manner allowing rotation and axial movement, rotatively driving means such as a hydraulic motor, a motor or the like for rotatively driving the injection screw, and a hydraulic injection cylinder unit for axially driving the injection screw. The screw-type resin injection apparatus is arranged as follows. That is, tile injection screw is rotatively driven about its own central axis by the rotatively drive means, whereby the resin is taken into the injection cylinder chamber by a screw pump action. The injection screw is forwardly driven axially by the injection cylinder unit, whereby the resin taken into the injection cylinder chamber is injected toward tile cavity in the forming mold by the resin injection nozzle.
In a conventional screw-type resin injection apparatus, a hydraulic injection cylinder unit for axially driving the injection screw is arranged in series relation to the injection cylinder element, axially of or on the same axis of the injection cylinder element, at a rearward end of the injection cylinder element. For this reason, an entire or overall axial length of the screw-type resin injection apparatus is lengthened in accordance with a requisite amount of axial movement of the injection screw. This obstructs miniaturization design of the screw-type resin injection apparatus, and largely obstacles compactification of the screw-type resin injection apparatus.
Further, generally, an injection screw used in the above-described in-line screw-type injection molding system has a screw-pump acting portion for executing a screw pump action, and a compound portion arranged forwardly more than the screw pump and gradually increasing as a diameter (minor diameter) of a bottom of a screw groove advances forwardly. A resinous material fed by the screw pump acting portion by rotation is kneaded while being compressed at the component portion.
The injection screw arranged as described above is suitable for injection molding of thermoplastic resin, but is not developed for a resinous material having a low viscosity. The injection screw tends merely to compress and mix the resinous material under a single stream or flow in the process of feeding the resinous material by the screw. For this reason, there cannot so be produced an excellent kneading action. This creates a problem in injection molding of a bi-liquid mixing resinous material such as silicon LIM. Particularly, there cannot be produced sufficient kneadability in injection molding of a resinous material of a low viscosity and bi-liquid mixing resin having a large viscosity difference.
Necessity occurs to lengthen an axial length of the injection screw, in order to increase the kneadability. However, extension of the axial length of the injection screw causes large-sizing of the in-line screw-type injection molding system.
Moreover, in the conventional injection screw, compression of the resinous material is executed in a compound portion so that the compound portion acts as a resistance of rotation of the injection screw. This increases the rotational resistance of the injection screw. In addition thereto, in a case where supply of the resinous material such as liquid resin having a low viscosity with respect to the screw portion is required to be forcibly executed by the use of a pressing or forcing unit, an increase in a required material supplying pressure is caused so that the necessity occurs in which the material supply pressure of the pressing unit is raised more than the resinous-material compressing pressure of the compound portion.
Further, it has been considered that, in order to improve the kneadability of the resinous material, a weir is provided at an intermediate portion of the injection screw to divide the injection screw into a plurality of zones in an axial direction.
This, however, also imparts a large or high resistance to the flow of the resinous material, to cause an increase in the required material supply pressure. Furthermore, the weir impedes the flow of the cleaning liquid at cleaning to deteriorate the cleanability within the injection cylinder chamber. Thus, washing away of the resinous material is not executed excellently.
In the injection molding of the bi-liquid mixing resin such as silicon LIM, there is a case where a static mixing mechanism is utilized, not relying upon an in-line screw, in order to mixing of the resinous material.
In a case of the static mixing mechanism, however, a long mixing head for mixing and a high material supply pressure are required because of the static divided mixing. If the resinous material is high in viscosity, a further high material supply pressure is required. Furthermore, there are disadvantage that mixing of a resinous material having a viscosity difference is difficult, and the injection molding apparatus is large-sized. Moreover, in a case of the static mixing mechanism, there is a limit or restriction that the resinous material must be one having a long pot life, because residence time in the mixing zone for the resinous material is long. Further, also in the static mixing mechanism, mixing of the bi-liquid mixing resin having a large viscosity difference is not sufficiently executed.
By the way, it has already been proposed that a gasket forming groove is formed in a Joining or Junction surface portion of the various articles, an uncured liquid gasket agent is filled in the gasket forming groove after assembling, and sealing is executed at the junction surface portion. The sealing of this kind is effectively applied to sealing of the junction surface portion of the various composition or constitutional elements in engines for vehicles or automobiles, electric equipments or instruments, general industrial machines and the like. Particularly, in the engines for vehicles, the sealing is applied to many locations, such as sealing of a junction surface portion between an engine block and a cylinder head cover, the junction surface portion between a transmission case and the engine block, the junction surface portion between an pan and the engine block, the junction surface portion between a timing gear cover and the engine block, the junction surface portion between an oil pump housing and the engine block, the Junction surface portion between a water pump outlet and an engine block, the Junction surface portion between constitutional parts of the differential gear case, and the like.
Conventionally, there has been an injection apparatus, as an apparatus for filling a liquid gasket agent into the gasket forming groove which is formed at the junction surface portion of the article. The injection apparatus is arranged such that the injection apparatus has a force feed pump and a liquid gasket agent supply hose connected to the force feed pump, wherein the liquid gasket agent is fed into the gasket forming groove from the nozzle at the forward end of the hose, through the liquid gasket agent supply hose by the force feed pump. This injection apparatus is disclosed in Japanese Patent Laid-Open No. HEI 2-203082.
In the injection apparatus arranged as described above, it is required that the nozzle at the forward end of the hose is detachably connected to and coupled to an injection port for the liquid gasket agent with respect to the gasket forming groove. This connection and coupling is executed by the fact that a male thread is formed on an outer periphery of the nozzle, a female thread is formed in an inner periphery of the injection port, and the male and female threads are screw-Joined to each other. This, however, is deteriorate in operability, and automatization is made difficult in a manufacturing line. Also in this case, the liquid gasket agent forcibly fed by the forcible feed pump reaches the gasket forming groove through the liquid gasket agent supply hose. Accordingly, a pressure loss is large or high, and there can only be produced an injection pressure of approximately a few tens Kgf/cm.sup.2. For this reason, in a case where a liquid gasket agent high in viscosity is injected, necessity occurs that an exhaust port is provided in addition to the injection port, and air within the gasket forming groove is sucked or drawn from the exhaust port by a vacuum pump, to assist fluidity of the liquid gasket agent within the gasket forming groove. If this necessity is not satisfied, the liquid gasket agent does not prevail over the entire gasket forming groove as a whole. Thus, a healthy or sound gasket is not formed.
Further, in the injection apparatus arranged as described above, a liquid gasket agent having rapid hardness such as a double-liquid reaction type cannot be used, because of avoidance of hardness of the liquid gasket agent in the liquid gasket agent supply hose, and a liquid gasket agent capable of being used is limited to a single-liquid liquid gasket agent such as a solvent volatile type and a humidity hardened type. However, these liquid gasket agents are isolated or cut off from outdoor air in the closed gasket forming groove and, accordingly, long time is required for hardening. This will cause reduction of productive efficiency. Furthermore, in addition thereto, a liquid gasket agent of heat hardening type can be used. This case, however, hardening of the liquid gasket agent in the gasket forming groove requires considerably long time also in this case, in order to lengthen a service life under a normal temperature.